The present invention pertains to a system comprising apparatus especially adapted to perform automatically a required calibration step so as to calibrate smoke detectors. More particularly, the present invention is directed to a system that accomplishes automatically both the required calibration and the retesting of such detectors such that they are assured of being completely reliable when placed in actual operation by a customer.
In order to furnish some background for the system or apparatus and to indicate the fundamental intent and purpose of such apparatus, reference may be made to a related patent application Ser. No. 647,018, which application involves a smoke detector featuring a balanced bridge network used to initiate an alarm when a difference is sensed between a pair of photocells which are effected by smoke obscuration in a chamber provided in such smoke detector. The bridge network is so arranged that two of the legs thereof are made up of the resistances of the aforesaid pair of photocells, these resistances normally being connected in series between a DC supply and ground. The other two legs of the bridge network are made up of selected portions of the total resistance of a potentiometer, which is likewise connected between the power supply and ground, the potentiometer being supplied with a movable contact for suitably proportioning the potentiometer resistance. It will be clear that the movable contact of the potentiometer is extended through the casing of the aforesaid smoke detector so that an external means such as a screwdriver may be used when an adjustment of the potentiometer resistance is required, as when calibrating the detector. For a detailed understanding of the operation of such a smoke detector, reference may be made of the cited application.
The present invention is particularly adapted to accomplish automatically the required adjustment which will provide calibration in the manufacturing stage of a smoke detector of the aforesaid type. However, it will be apparent to those skilled in the art that the present invention is not strictly limited to the precise type of smoke detector referred to above and can be used in connection with a variety of smoke detectors that have similar adjustment or calibration arrangements.
In any event, regardless of the particular type of smoke detector whose calibration and testing is under consideration, the fact is that uniform standards have been completely lacking in the calibrating and testing of smoke detectors of current design. Thus each manufacture tends to follow his own bent in calibrating and testing such detectors and this has led to severe difficulties when such units are placed into operation by customers. For example, the rate of flow of the smoke that is furnished in the testing operation has often not been carefully controlled with the result that time lags and the like render questionable the precise obscuration levels at which the smoke detectors went into an alarm state.
Accordingly, it is a primary object of the present invention to provide automatic apparatus for the aforesaid purposes such that a high degree of reliability will be assured in the calibration and testing operations.
Another object is to establish control on the degree of smoke obscuration present in a testing chamber. More specifically, it is an object of the invention to increase visible smoke obscuration automatically at an approximate uniform rate of 0.4% per foot per minute.
It is well understood that smoke detectors of current design are often so calibrated that they are meant to respond to smoke obscuration at levels typically between 1.34% and 1.55%. However, as previously noted, the methods and techniques used for calibrating smoke detectors have left much to be desired and it is to the end of proper and precise calibration that the smoke obscuration is automatically increased at a predetermined rate, preferably the aforesaid 0.4% per foot per minute rate. As a result, it is insured that the smoke detectors calibrated and tested in accordance with the present invention will provide the required alarm when they reach the aforementioned range of smoke obscuration.
In essence then, the above objects of the invention are implemented by a primary feature residing in the provision of apparatus comprising an enclosure defining a smoke chamber, such smoke chamber including a reserve smoke compartment for generating a large quantity of reserve smoke, a smoke mixing compartment in which the dense smoke from the reserve compartment is permitted to diffuse and to be drawn in a path which brings a uniform smoke of required density into a test compartment in which a plurality of groups of smoke detectors to be calibrated and tested are disposed.
In the initial determination of the degree of light obscuration that has been achieved by the smoke that has been drawn in, a light source and a photocell are used. Thus the photocell is connected in a suitable circuit that operates to provide a current output equivalent to the smoke level at any time. In addition, from the standpoint of the broad aspect of the present invention, means are also provided for automatically changing the degree of light obscuration produced by the influx of smoke by changing the flow of smoke into the aforenoted test compartment. This means for automatically changing the degree of obscuration includes means for so increasing the obscuration at a precise and predetermined uniform rate. Preferably this rate has been selected to be 0.4% per foot per minute.
Over and above the immediately above-noted components or features, the present invention, in addition to efficiently accomplishing the objective of providing a precise and uniform rate of increase in the obscuration level, achieves the further objective of automatic calibration by including means for increasing the light obscuration to the predetermined calibration range, that is, the range in which a smoke detector device under test should respond and provide the appropriate alarm indication. Further provided are means for calibrating groups of smoke detectors under test by the provision of means for adjusting each of the smoke detectors as the smoke obscuration level reaches the calibration range such that the smoke detectors under test will normally provide their alarm indication. To this end a further feature resides in means which are provided for indicating to the operator whether each detector has in fact been properly calibrated, that is, has given its alarm indication at the appropriate point.
A further specific feature resides in the provision of achieving the precise adjustment required in calibrating the smoke detectors by an arrangement including means within the apparatus for engaging each of the potentiometer contacts, preferably by a screwdriver driven by an individual motor for each of the detectors. Further included is a control arrangement on the synchronous motors so that they are turned counterclockwise to reach a zero position on the command of suitable electric components and are then, at the appropriate calibration time, turned clockwise until a point is reached when the detector correctly gives its alarm indication. Whether or not each detector has given its alarm is monitored by a probe or similar device and a display indication is given to the operator of such successful calibration.
It is a further specific feature of the invention that independent flow channels are established for each of the groups of detectors under test. That is to say, when the smoke is being brought in for the purpose of calibrating and testing these detectors, the arrangement is such that the smoke is swept in by the operation of fans and uniform flow is promoted by a baffle assembly, the baffle assembly being so constructed that the flow of smoke is divided into independent channels and this channeling is preserved when the smoke is brought past the detectors which are arranged on a tiered or multi-level basis. Preceding the tiered basis or arrangement is a honeycomb device which further insures uniformity of the smoke mixture in each of the channels.
Yet another feature of the present invention resides in a technique, subsequent to carrying out the calibration of the smoke detectors, of exhausting the smoke used in the calibration stage, that is to say, of completely venting the enclosure; and thereafter instituting a test cycle which can be carried out in a much shorter time period inasmuch as one does not have to perform the operation of making the potentiometer adjustment, as in the calibration stage or cycle. Rather, one simply wants to check to determine if the calibration was done properly such that the devices again respond when the smoke obscuration reaches the predetermined level.
Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the annexed drawing, wherein like parts have been given like numbers.